1. Field of the Invention
The present invention relates to an antireflection film used in order to suppress decrease of the screen visibility of a visual display, such as in liquid crystal displays (LCD), organic EL displays and PDP, and to an optical element having the antireflection film concerned prepared thereto. Moreover, the present invention also relates to a visual display with the antireflection film or the optical element concerned provided thereto. Furthermore, it relates to an antireflection layer forming agent, and an antireflection layer formed by the antireflection layer forming agent.
2. Description of the Prior Art
Research and development in recent years, a liquid crystal panel device is ensuring steadfast status as a display. However, in monitors for car navigation system and in monitors for video cameras, which is used with high frequency in brightly illuminated environment, decrease in visibility caused by surface reflection is notably observed. Therefore, it is becoming indispensable that antireflection processing is applied to polarizing plates used for liquid crystal panel devices. Polarizing plates with antireflection processing applied thereto is used for most of liquid crystal displays having high operating frequency in outdoors.
Generally in antireflection processing, multi-layer laminated body of two or more thin films comprising materials having different refractive indexes is produced by dry processing methods, such as vacuum deposition method, sputtering method, and CVD method, and thus design is adopted for reducing reflection of visible light region as much as possible. However, in formation of thin film by the above-mentioned dry processing, a vacuum facility is required, consequently leading to very expensive processing costs. Therefore, in recent years, antireflection films are produced to which antireflection processing is performed by formation of antireflection film by a wet coating process. In antireflection films, a constitution comprising, a transparent substrate used as substrate/a resin layer for granting hard coat property/an antireflection layer with low refractive index, is usually adopted. In these antireflection films, in the viewpoint of reflectance, a hard coat layer requires a higher refractive index and an antireflection layer requires a lower refractive index.
As a material having a low refractive index for forming the above described antireflection layer, in the viewpoint of refractive index or stain resistance, polymers containing fluorine etc. are used. Moreover, in general, some approach is performed where porous structures are obtained utilizing a sol-gel reaction of alkoxy silanes or organo alkoxy silanes as material giving a lower refractive index to provide a lower refractive index. However, in the above-mentioned sol-gel reaction, when baking at low temperature is performed in order to control reactivity and to obtain porous structure, long reaction period is inevitably required in curing process, and consequently an antireflection layer having sufficient scratch-proof property cannot be formed in a short period of time. Moreover, film surfaces given by the above-mentioned sol-gel reaction have problems also in stain resistance.
Moreover, in Japanese Patent Laid-open Publication No. H9 (1997)-208898, a proposal using fluorine compounds containing a polysiloxane structure for an antireflection layer is disclosed. In formation of an antireflection layer with the fluorine compounds, uniform reaction is performed, and this method is excellent in stability of liquid, and film uniformity after cured, and good also in stain resistance. However, the fluorine compounds have a little slow curing rate of reaction, and therefore curing requires a long period of time in baking at low temperature. Baking at high temperature is not acceptable, for example, as in a case where triacetyl cellulose film preferably utilized as a protective film of polarizing plate is used as a transparent substrate, and an antireflection layer with the above described fluorine compounds is formed through a hard coat layer thereon. Curing (ageing) time of several days at a temperature of approximately 100 degree C. is required in order to obtain sufficient scratch-proof property.
The present invention is providing an antireflection film having a hard coat layer prepared thereto and an antireflection layer with a low refractive index laminated onto a surface of the hard coat layer of a transparent substrate by coating method, wherein an antireflection layer having excellent scratch-proof property and stain resistance by curing process performed in a short period of time at comparatively low temperature is formed. It also is providing an optical element in which the antireflection film concerned is prepared. Moreover, it is providing a visual display with the antireflection film concerned or the optical element provided thereto. Furthermore, it is providing an antireflection layer forming agent and an antireflection layer formed by the antireflection layer forming agent concerned.
As a result of whole-hearted examinations made by the present inventors to solve the above described problems, it was found out that the above described objective might be attained using an antireflection film given below, thus leading to completion of the present invention.
That is, the present invention relates to an antireflection film having a hard coat layer prepared on one side of a transparent substrate directly or through other layers, and further an antireflection layer laminated on a surface of the hard coat layer,
wherein the antireflection layer is formed by a dry cured film obtained from a solution comprising
a siloxane oligomer (A) obtained by condensation polymerization after partial hydrolysis of a hydrolyzable alkoxy silane that contains a tetra alkoxy silane represented by a general formula (1): Si(OR)4 (where R represents methyl group or ethyl group) as a principal component
and a compound (B) having a fluoro alkyl structure and a polysiloxane structure.
In the above described antireflection film of the present invention, stain resistance is improved using the above described compound (B), and simultaneously the siloxane oligomer (A) being blended thereto, a slow curing speed of a polysiloxane in the compound (B) having low reactivity is compensated by the reactivity of the siloxane oligomer (A) blended. In this way, when a sol-gel coating material (coating liquid) of a type controlling reactivity in the course of thin film formation is used, an antireflection layer having good scratch-proof property and stain resistance may be formed even in a short curing time at a comparatively low temperature, and, as a result, an antireflection film may be obtained with sufficient productivity.
Moreover, adhesion between the antireflection layer having a low refractive index and the hard coat layer formed in this way improves as compared with an antireflection layer in which the siloxane oligomer (A) or the compound (B) is used independently. Therefore, in reliability test of adhesion etc., peeling will not be observed at an interface between the hard coat layer and the antireflection layer.
In the above described antireflection film, it is preferable that the above described siloxane oligomer (A) is blended, as a dry cured compound in a dry cured film formed as an antireflection layer, so that solid content weight ratio may give 10 to 80 percent by weight in the above described solution for forming the antireflection layer.
The above described siloxane oligomer (A) has high reactivity and when this is independently used for formation of an antireflection layer, an uneven film may easily formed and the film has high density. Therefore, a value of refractive index gives nd20 (refractive index of 20xc2x0 C.)=1.45 order, then leading to raise of reflectance (dependent on refractive index). Therefore, in formation of the antireflection layer, in viewpoint of balance of reflectance and promotion of curing, it is preferable that the above described mixing ratio of the above described siloxane oligomer (A) is 10 to 80 percent by weight. The above described mixing ratio of the above described siloxane oligomer (A) is more preferably 20 or more percent by weight from a view point of curing promotion. A higher mixing ratio concerned gives formation of a more dense film, and simultaneously a film strength also rises. On the other hand, in the viewpoint of realization of low reflectance, the above described mixing ratio of the above described siloxane oligomer (A) is preferably 80 or less percent by weight, more preferably 50 or less percent by weight, and still more preferably 40 or less percent by weight. In addition, generally in antireflection layer (low refractive index layer), the above described refractive index is preferably about 1.45 or less, and more preferably 1.41 or less. Moreover, reflectance is preferably about 3 or less percent, and more preferably 2.5 or less percent.
In the above described antireflection film, a hard coat layer is preferably formed of an ultraviolet curable resin, and nd20 (refractive index at 20xc2x0 C.) is preferably 1.49 or more.
Curing processing with an ultraviolet curable resin is an easy processing operation, and, thereby, a resin coated layer can be efficiently formed in formation of a hard coat layer. Moreover, a refractive index nd20 (refractive index in 20xc2x0 C.) of this hard coat layer is preferably 1.49 or more, and more preferably 1.52 or more so that while an antireflection layer of low refractive index may keep a low refractive index.
In the above described antireflection film, it is preferable that the surface of the hard coat layer has uneven form, and thus has optical antiglare property. Moreover, in the above described antireflection film, it is preferable for fine particles to be included in the hard coat layer.
When given uneven surface form to the surface, the hard coat layer may demonstrate function as an antiglare property film having also optical diffusion. Moreover, a resin coated layer that has uneven form on the surface is simply and reliably realized using fine particles.
And the present invention relates to an optical element characterized by the above described antireflection film prepared on one side or both sides of an optical element. An antireflection film of the present invention may be used for various kinds of applications, for example, for optical elements. A polarizing plate laminated with the antireflection film of the present invention thereon is excellent not only in antireflection function but in hard coat property, scratch-proof property, and durability, etc.
Furthermore, the present invention relates to the above described antireflection film or a visual display with the above described optical element provided thereto. An antireflection film of the present invention and an optical element are used for various kinds of applications, for example, they are installed on a top face etc. of a visual display.
And the present invention relates to an antireflection film forming agent comprising a solution including a siloxane oligomer (A) obtained by condensation polymerization after partial hydrolysis of a hydrolyzable alkoxy silane that contains, as a principal component, tetra alkoxy silane represented by a general formula (1): Si(OR)4 (where R represents methyl group or ethyl group), and a compound (B) having a fluoro alkyl structure and a polysiloxane structure. And, it is also related to an antireflection film formed by a dry cured film of the antireflection film forming agent concerned.